As you all know in 3.1 the quest tracker and achievement frame share the same space. I use questsfu for the darker background coloring of the quest frame, but this feature utilizes a custom tracker frame and turns off the default blizzard quest/achievement tracking frame. I don't want to change from using this mod as it's very lightweight for my present needs.
For me this leaves a space that needs to be filled. I hope that it's possible to make a frame that is capable of watching and tracking at least one achievement separate from the quest log. It's fine if it looks like it does currently (no fancy bar graphics/shapes etc). I'm just looking to have it be visible and movable, on screen.
I know you said you didn't want to change from QuestsFu, but you might like to have a look at InQuest, which I believe will replace QuestsFu for you as it tracks both Quests and Achievements. It's also pretty lightweight.
EDIT: For comparison, it's apparently using about 180K of memory on my machine at the moment.
I'll check it out, but seems to be lighter than what I need. Questsfu allows me to mouseover and select which quests I want to track without the need to open the default questlog.
if you wish there is also tomQuest2 (I'm the author)
it is a native ldb addon. It does quest and achievement tracking in two independant frame that you can put where you want, hide in combat if you wish...
It was inspired by questFu so you should find almost all functionality from questFU and more